Michel Barnier's comments that Brussels is "ready to improve" the text of the Irish backstop is part of a "conciliatory tone" towards Britain, senior Brexit sources have said.

Mr Barnier, the EU chief negotiator, yesterday signalled a willingness to be somewhat flexible in Brexit negotiations around the Northern Irish border.

Sources have indicated that any alterations will "not change the substance of the Irish backstop". The backstop is the default position if the UK leaves the EU without a deal.

Calling the issue "the biggest risk" caused by Brexit, Mr Barnier said he was "ready to improve" the text of EU's version of the backstop.

The EU published its interpretation of the plan in February, but it was roundly rejected by Prime Minister Theresa May and her government.

It kept Northern Ireland within the regulatory area of the EU's customs union in the event that EU and UK fail to reach a trade agreement comprehensive enough to negate the need for a customs or regulatory border.Mrs May said the EU's proposal "annexed" Northern Ireland, and thereby interfered with the constitutional integrity of the UK.

Subsequently in March, and in various recent speeches, Mrs May has reaffirmed the UK's commitment to a backstop, but said she would come up with her own legal definition of it.

Mr Barnier said: "Since we will not know what the future relationship will bring by autumn 2018, we need to have a backstop solution in the withdrawal agreement. The UK agrees with this, and both the EU and the UK have said that a better solution in the future relationship could replace the backstop.

"What the EU has proposed is that Northern Ireland remains in a common regulatory area for goods and customs with the rest of the EU. We are ready to improve the text of our proposal with the UK."

The UK Government issued a document in May which attempted to deal with preventing a hard border in the case of no deal - effectively their backstop plan.

However, it was deemed incomplete and inadequate as it did not address important single market regulations.

A source said: "The backstop has to be all-weather, has to prevent a hard border - no matter what, and is now even more important as time ticks on." In an op-ed paper clearly aimed to cool Brexit brinkmanship, Mr Barnier also struck a positive tone about reaching a deal "unprecedented in scope and depth" around free trade with the UK.

But he warned that UK proposals must not "undermine" the four pillars of the single market - free movement of goods, capital, services and labour, by seeking freedom only for goods.

Meanwhile, Sinn Fein must take their seats in the House of Commons and help minimise the impact of Brexit on Ireland, an Irish politician has warned.

Fine Gael senator Neale Richmond repeated calls for the party's MPs to take their seats in Westminster, stressing that any Brexit deal gets through the House of Commons as well as the European Parliament.

He said: "Hiding beyond the mantra of abstentionism is no longer credible. It is not a sacred cow that is above analysis or indeed a change of opinion."

Last week Sinn Fein deputy leader Michelle O'Neill ruled out any change to the absentionist policy, describing suggestions to the contrary as "a wee bit of nonsense".